: A comparison of casuistry with the strain of particularism developed by John McDowell and David Wiggins suggests that casuistry is susceptible to two very different mistakes. First, as sometimes developed, casuistry tends toward an implausible rigidity and systematization of moral knowledge. Particularism offers a corrective to this error. Second, however, casuistry tends sometimes to present moral knowledge as insufficiently systematized: It often appears to hold that moral deliberation is merely a kind of perception. Such a perceptual model of deliberation cannot offer a convincing account of the possibility of moral progress. This second problem is one to which particularism is itself prone. To redress it, other aspects of casuistry must be exploited: Casuistry contains an account of presumptive generalizations that explains how moral deliberation might be structured by rules while also depending at critical junctures on perception